I find it strange iplboot fails with sd2sp2, it uses the same code for slot A, B and sd2sp2 devices. I can't recompile right now since I don't have clang on my windows setup.

I have tested IPLBoot a little more so:
Slot B: writes a lot of things in a black screen before launching SWISS
SP2: reboots immediately to GC's IPL
SP2 with empty SDGecko: writes three lines, wait a little, then reboots the console

Hope this will help, don't hesitate to ask if there is anything more I can do to help.

It's not as if we have the choice, as long as this iplboot is not fully operationnal, and Ledu205's version is not small enough to fit on a chip.
If only you can compress the dol with dolxz just before converting it to GCI, it may be wayyy smaller, and I may use it again. Not that space is hard to find on my memcards, but I already tested the big version, and I'll only replace Ledu205's by something "new".